The present invention relates to a printer having a thermal head for acting on a thermally sensitive paper, or for transferring an ink film or the like to a record paper.
Conventionally, as shown in FIG. 4, an FPC (Flexible Printed Circuit) 53 having a circuit pattern 54 on a polymide film is utilized as a connector circuit for leading a circuit terminal 52 formed on a thermal head substrate 51 to an external thermal head control circuit. The FPC 53 is connected to the circuit terminal 52 by soldering or by means of an adhesive 55 having dispersed electroconductive particles in a known thermal head construction.
For example, Japanese Utility Model Application Laid-open No. 2-115447 discloses such a construction of the thermal head where the FPC and the circuit terminal are coupled with each other by adhesive having dispersed electroconductive particles. In such a construction, the adhesive 55 containing the dispersed electroconductive particles or a solder has a function to provide an electrical contact between the circuit terminal 52 and the circuit pattern 54 of the FPC 53, and another function to mechanically fix the FPC 53 and the thermal head substrate 51 with each other. In this case, the circuit terminal 52 is generally formed of a cheap metal film such as aluminum, aluminum alloy and copper. Alternatively, in case of the soldering connection, the circuit terminal 52 has a copper surface or the like of is metalized by nickel in a general structure. On the other hand, in case of the coupling by means of the adhesive containing the dispersed electroconductive particles, as described in the Japanese Utility Model Application Laid-open No. 2-115447, the electroconductive particles dispersed in the adhesive are pressed into the surface of the circuit terminal 52 to provide the electric contact to the circuit pattern of the FPC 53, while the connection is secured and fixed by means of the adhesive. Accordingly, a surface treatment is not required for the circuit terminal 52, and therefore the connecting treatment may be applied directly to the exposed aluminum or copper film.
However, the conventional thermal head having the above described construction has problems as follows.
(1) The circuit terminal 52 of the thermal head substrate 51 has a free noncontact area 52A which is exposed in the vicinity of the contact area to the FPC 53. Further, the exposed area has a surface composed of the circuit terminal materials such as aluminum and copper, or composed of nickel metalization applied to the circuit terminal. These metal materials are quite corrosive when exposed to the atmosphere containing moisture or active gas.
(2) The thermal head substrate 51 and the FPC 53 are overlapped with each other along a narrow width portion where the connection is held by the solder or the adhesive. Accordingly, the connected portion has a rather weak mechanical strength. When an external force is applied to the connected portion, the thermal head may suffer from serious malfunctions such as a crack or peeling at the connected portion.
(3) When a foreign material such as metal chips is dropped onto the exposed noncontact area 52A of the circuit terminal 52, a short-circuit may occur by the foreign material to cause operation failure or mis-operation.